Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$78.90	9.816%	$86.6448	$86.64	$86.65	$86.60
Purchase #2	$16.48	12.527%	$18.5444	$18.54	$18.55	$18.50
Purchase #3	$47.59	6.753%	$50.8038	$50.80	$50.80	$50.80
Purchase #4	$90.55	12.472%	$101.8434	$101.84	$101.85	$101.80
Purchase #5	$46.40	8.412%	$50.3032	$50.30	$50.30	$50.30
Purchase #6	$11.29	5.828%	$11.948	$11.95	$11.95	$11.90
Purchase #7	$93.32	7.792%	$100.5915	$100.59	$100.60	$100.60
7 purchase totals =	$384.53		$420.6791	$420.66	$420.70	$420.50